The present invention is directed to an optical electrical device or component for outfeed and infeed of radiation which is guided in a waveguide.
Light is used in optoelectronic devices (OED) either as a signal carrier or as an energy carrier. In order to exchange signals or, respectively, to exchange energy between various elements, the light must be transported. A coupling between a transmitter and a receiver is needed for this purpose. This can occur either via waveguides, such as optical fibers, or through space, which does not require any waveguides. In each instance, however, light must be outfed from or, respectively, infed into the electronic component.
The coupling of radiation through the substrate is possible in OEDs when the substrate is transparent for the emitted light. The vacuum wavelength must be greater than 0.9 .mu.m for GaAs and InP substrates and must be greater than 1.1 .mu.m for Si substrates. Given an arrangement wherein light is coupled through the substrate, the electronic and optical coupling can be distributed onto two separate planes or levels. It is also not necessary, in this case, to conduct the light with the waveguides at the edge of the substrate. Greater freedom in the arrangement of the optoelectronic device is, therefore, achieved.
The prerequisite for a separation of the electrical from the optical coupling is that a technology is made available that assures that the light departs the substrate at exactly defined angles. Great losses of optical intensity, however, will occur, and these must be reduced by individual mounting of the individual optoelectronic devices. The advantage mentioned in the offset would, thus, be lost. Since the orientation of the crystal planes is multiply exploited during the manufacturing process of each and every optoelectronic device because the exploited effects depend thereon, the direction perpendicular to the waveguide is available for the definition of the exit angle. The distributed feedback along the waveguide with the assistance of a DBR grating can be employed in order to couple light out in this way. The coupling between an optoelectronic device and an optical fiber, however, is more beneficial when the transverse electromagnetic field distribution of the light beamed out perpendicular to the waveguide is critically defined by the guidance property of the waveguide. In this case, the beam must be deflected at a mirror having an angle of inclination of exactly 45.degree. relative to the waveguide. The demand of high smoothness is also made of this mirror, for example the roughness of the mirror surface must be low in comparison to the wavelength of the radiation. Up to now, mirrors that are extremely smooth in the optical sense have been capable of being realized only on the basis of mirror breaking, as well as dry etching and subsequent wet etching. Since mirror breaking in this direction at an angle of 45.degree. relative to the waveguide is impossible for crystallographically reasons, only etching remains as a possibility. Dry etching is usually possible independent of the crystal orientation, but supplies roughened mirrors so that an after-treatment with an etching step is required. Like breaking, wet etching itself usually only succeeds along crystallographically pronounced planes or respective directions.
After the exit of the light from the substrate, a pronounced widening of the light ray will occur due to refraction phenomena. This is countered in the traditional technology in that a light is focussed by a spherical lens which precedes the optical fiber. The arrangement, therefore, successively comprises the optoelectronic device, a spherical lens and the optical fiber.
The coupling of optical energy in optoelectronic devices generally occurs in the direction of the waveguide on the basis of the optical mirrors that are arranged orthogonically relative thereto. Coupling perpendicular to the waveguides is hereto undertaken with the assistance of a DBR grating on the basis of the distributed feedback or with the assistance of a mirror inclined at 45.degree. relative to the waveguide. In this respect, see the article by Z. L. Liau, J. N. Walpole, L. J. Missaggia and D. E. Mull entitled "GaInAsP/InP buried-heterostructure surface-emitting diode laser with monolithic integrated bifocal microlens" Appl. Phys. Lett, Vol. 56, No. 13, Mar. 26, 1990, pp. 1219-1221; the article by Z. L. Liau and J. N. Walpole entitled "Surface-emitting GaInAsP/InP laser with low threshold current and high efficiency", Appl. Phys. Lett, Vol. 46, No. 2, Jan. 15, 1985, pp. 115-117; the article by J. N. Walpole entitled "R&D on Surface-Emitting Diode Lasers", Laser Focus/Electro-Optics, September 1987, pp. 66-74; the article by H. Saito and Y. Noguchi entitled "A Reflection-Type Surface-Emitting 1.3 .mu.m InGaAsP/InP Laser Array with Microcoated Reflector", Japn. Journal Appl. Phys., Vol. 28, No. 7, July 1989, pp. L1239-L1241; the article by M. Mihara entitled "New Surface-Emitting Laser Diode Connects to Optical Fiber Directly", JEE, Hi-Tech Report, June 1989 pp. 74-77; the article by J. P. Donnelly, R. J. Bailey, C. A. Wang, G. A. Simpson, and K. Rauschenbach entitled "Hybrid approach to two-dimensional surface-emitting diode laser arrays", Appl. Phys. Lett., Vol. 53, No. 11, Sep. 12, 1988, pp. 938-940; and an article by K. Iga, F. Koyama and S. Kinoshita entitled "Surface-Emitting Semiconductor Lasers", IEEE Journ. Quantum Electron., Vol. 24, No. 9, September 1988 pp. 1845-1855.
With the exception of the publications by Z. L. Liau et al, the outfeed in these known arrangements does not occur through the substrate. In the cited exception, the volume of the substrate belongs to the resonance space of the laser. The resonance condition of the laser is defined here by a mirror orthogonally vis-a-vis the active waveguide and by the mirroring substrate underside. In order to enable laser operations and, therefore, feed light out, the effective reflection of the substrate underside in this arrangement must be increased by a metal coat that, however, only partially extends over the lens. The metal coat has a round opening in the middle of the lens. The round surface of the integrated lens is achieved by etching a plurality of concentric mesas and by subsequently rounding the mesa steps with the assistance of mass transport.
The mirror inclined at 45.degree. relative to the waveguide is produced in a similar way. For example, see the article by Z. L. Liau and J. N. Walpole.